Atmospheric pressure ionisation techniques such as electrospray and chemical ionisation are used to generate ions for analysis by mass spectrometers. Ions created at atmospheric pressure are generally transferred to high vacuum for mass analysis using one or more stages of differential pumping. These intermediate stages are used to pump away most of the gas load. Ideally, as much of the ion current as possible is retained. Typically, this is achieved through the use of ion guides, which confine the trajectories of ions as they transit each stage.
In conventional mass spectrometer systems, which are based on components having dimensions of centimeters and larger, it is known to use various types of ion guide configurations. These include multipole configurations. Such multipole devices are typically formed using conventional machining techniques and materials. Multipole ion guides constructed using conventional techniques generally involve an arrangement in which the rods are drilled and tapped so that they may be held tightly against an outer ceramic support collar using retaining screws. Electrical connections are made via the retaining screws using wire loops that straddle alternate rods. However, as the field radius decreases, and/or the number of rods used to define the multipole increases, problems associated with such conventional techniques include the provision of a secure and accurate mounting arrangement with independent electrical connections. For similar reasons, the provision of a quadrupole configuration for mass filtering applications requires a mounting arrangement that can provide the necessary tolerances and accuracy.
There is, therefore, a need for a means of accurately producing multipole configurations for use in microengineered systems, specifically for use in mass spectrometry applications.